Howling is an oscillation phenomenon caused by a sound loop in which a sound outputted from a speaker returns to a microphone. Once a sound loop is formed, a sinusoidal signal having a sharp peak is generated and a sound having a particular frequency continues to be amplified until the loop is cut.
As a conventional howling suppression device, there is proposed one which estimates spatial transfer characteristics between a microphone and a speaker by adaptive processing using an adaptive filter, and cuts a sound loop by subtracting a pseudo feedback signal produced by the adaptive filter from an input signal, thereby suppressing a howling sound (see Patent Literature 1 for an example).